This invention relates to temporary and permanent medical catheters such as are used, for example, in heart pacemaker and defibrillator therapy as well as in electrophysiological research.
Medical catheters are used either as diagnostic catheters with pure detection function or as therapeutic catheters with detection, stimulation and ablation function with high frequency energy, hereinafter referred to as HF energy. It is conceivable that the present invention can be used with both non-guided and guided catheters. The construction of such prior art catheters has, in principle, been the same for decades, and include:
Shell-shaped electrodes made of stainless steel or Pt/Ir are drawn over a plastic hose with cavities which is made of, for example, PVC, nylon, polyurethane or similar material, and connected to wires located in the interior of the catheter for the conveyance of electrical energy.
A typical electrode size is, for example, 6F (1F roughly corresponds to 0.33 mm) with a shell or electrode length of 2 to 10 mm. While diagnostic usually have a certain specified curvature at their distal ends guided catheters in the rest state are initially straight and can be brought to a desired curvature from the distal end by the operator, such curvature sometimes far exceeding a 90xc2x0 angle with a radius of curvature of 2 to 4 cm.
The objective of this pre-curvature or pre-bending is to achieve a certain wall contact in the heart or in another body part, depending on the application, in order to improve the extracted signal strength or, when the electrode is a stimulation or ablation electrode, to guarantee optimal energy transfer by good wall contact with the tissue. In ablation with HF energy, in particular, the geometrical dimensions of the electrode shells, or of the so-called electrode head, also called electrode tip, takes on special importance. In what follows, the electrode configuration according to the invention is explained for the example of an ablation catheter; however, the invention is suitable for other applications.
In usage, an ablation catheter is pressed against the tissue at a certain location in the body by appropriate manipulation, by stiffness of the catheter itself, by an appropriately selected pre-curvature or, in the case of guided catheters, by a curvature that is operator controlled.
If body tissue is also yielding, only a certain part of the electrode shell or of the electrode tip comes in intimate contact with the tissue, while the other part of the electrode comes to lie more-or-less without wall contact and is then inevitably bathed by tissue fluidxe2x80x94thus by blood, in the case of ablation catheters for cardiological application. Because blood exhibits a lower resistance than tissue, the energy delivered is distributed according to the resistance ratios. This leads to the surrounding blood being undesirably heated instead of the HF energy being directed to the tissue in order to produce the appropriate desired lesions there.
An electrode configuration addressing this problem is disclosed in U.S. Pat. 5,643,255 for a Steerable Catheter with Rotatable Tip Electrode and Method of Use issued on Jul. 1, 1997 to Leslie W. Organ. In this prior United States patent, a tip electrode is provided on a catheter which is insulated on one side and rotatably supported so that the electrode position can be adjusted from outside in such a way that the uninsulated surface comes in contact with the tissue to be ablated and thus the desired ablation result is brought about. To insulate parts of an electrode surface, however, requires a relatively expensive manufacturing process.
So-called split electrodes are also known, which have an electrode shell split in two on the longitudinal axis or which have an electrode head split into four parts.
The individual electrode elements in the above-cited cases must be electrically insulated relative to one another. In these prior catheter concepts, the mechanical arrangement of the electrode shells on the plastic hose is difficult to accomplish.
It is an object of the invention to create an electrode configuration that, on the one hand, guarantees favorable electrical properties and, on the other hand, is easy to manufacture and guarantees reliable mechanical functioning.
While, in the previously known electrode shells, the entire surface is in operative connection with the media surrounding it, it is proposed according to the invention that the electrode shell or the electrode tip has cutouts of predetermined size and shape. These cutouts can be in the form of a single hole or multiple holes, slots, perforations, or milled grooves of predetermined curved shape. It is important, however, that an electrode shell whose surface has been reduced in this way can be attached to the plastic hose in the proven manner. According to the invention, this is guaranteed by virtue of the fact that the cutouts are arranged such that at least one electrode shell ring, enclosing the catheter hose in circular fashion is present.
The electrode tip attached to the distal end of the catheter includes an electrode shell with its distal end closed by a cap to form an electrode point.
The cutout according to the invention is arranged such that the electrode tip shell has at least one closed electrode ring required for strength; the electrode ring being arranged, for example, at the proximal end of the tip shell. In order, however, to guarantee that the electrode tip still has a firm grip on the plastic hose at its distal end, the cutout should, according to the invention, be arranged such that the electrode cap extends circumferentially around the end of the catheter hose, so that a further closed distal xe2x80x9cringxe2x80x9d is created.
The electrode configurations brought about by the before mentioned cutouts have reduced areas. These remaining residual areas should preferably face toward the tissue being treated. It is therefore proposed that these residual areas be arranged essentially on the outside of the catheter curvature in the case of pre-bent or externally bendable catheters.
According to a preferred embodiment of the invention, sensors for energy control are placed in the plastic hose and/or beneath the electrode shell at the transitions from the cutouts to the electrode surfaces. These are preferably temperature probes for the control of the catheter temperature in HF energy ablation.
In further development of the invention it is proposed that instead of a circular configuration of the catheter hose, as well as the electrode shell and the electrode tip, it is made elliptical, at least in portions. This variant has the advantage that the overall catheter arrangement has a flexurally soft direction of curvature and a flexurally stiff direction of curvature. As is well known, an elliptical section hose bends easier in one direction than in a direction at right angles to the one direction. For the user, this concept has the advantage that the user can exert greater pressing forces in the flexurally stiff direction. In line with this, it is further proposed that the residual surfaces of the electrode shell left over by a corresponding cutout are arranged on one of the elliptical catheter sides with the tighter radius of curvature.
The electrode shell is easier to manufacture if the cutout is made such that only a closed circular ring and a contact surface with a free end is the resulting configuration. Two or more such electrode shells are then arranged on a catheter hose in such a way that the free end of one such electrode shell comes to lie beneath the closed circular ring of the neighboring electrode shell.
It is proposed that several electrode-shell configurations are also interlocked or chained in such a way that they form, for example, tripolar or quadripolar configurations.
In further development of the invention it is proposed that the entire external or internal surface of the closed circuit ring be provided with an insulating layer. The insulating layer applied to the inside of the ring then serves for electrical insulation relative to the contact surface of a neighboring electrode shell; the externally arranged insulation prevents the surface of the closed circular ring being added to the total contact surface.